There have been proposed many methods for obtaining a positive dye image through a diffusion transfer process. For example, it has been proposed to form a positive dye image by using a system combining a reducible dye donating compound which is capable of releasing a dye with a reducing agent or a precursor thereof, in which wet development or heat development is effected to oxidize the reducing agent in proportion to the exposure amount of silver halide while reducing the dye donating compound with the portion of the reducing agent which remains non-oxidized to thereby release a diffusing dye, as disclosed in U.S. Pat. Nos. 4,559,290, 4,356,249, and 4,358,525, JP-A-53-35533, JP-A-53-110827, JP-A-54-130927, JP-A-56-164342, JP-A-59-154445 and JP-A-62-215270 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Further, European Patent Publication No. 220,746 and Kokai-Giho 87-6199 [Vol. 12, No. 22) disclose a heat-developable color light sensitive material using a nondiffusing compound which releases a diffusing dye through a similar mechanism, the nondiffusing compound being capable of releasing a diffusing dye through reductive cleavage of an N-X bond (X represents an oxygen, nitrogen or sulfur atom).
However, when the above-described reducible dye donating compounds are used in combination with a silver halide emulsion together with a reducing agent or a precursor thereof, it has turned out that the developed dye image suffers from considerable stain formation and also such light-sensitive materials have poor preservability before use.
In order to suppress stain formation of the light-sensitive materials for positive image formation using the reducible dye donating compounds, it is effective to use a diffusing electron transport agent in addition to a nondiffusing electron donor as a reducing agent. On the other hand, a radical resulting from the electron transport agent diffuses into other layers having different color sensitivity to cross-oxidize the electron donor present in that layer, thereby causing reduction of image density and deteriorating color reproducibility. Hence, it has been attempted to provide an intermediate layer between light sensitive layers differing in color sensitivity or incorporate a reducing substance in such an intermediate layer. The light-sensitive materials which can be used in a diffusion transfer process, such as those used in the present invention, have limitations with respect to the amounts of binders and reducing substances which can be used in each layer, with image formation rate, resolving power, and film properties being taken into consideration. Further improvements have therefore been demanded.